Process for manufacturnig an internally cooled valve having a cooling structure, and valve manufactured by said method

ABSTRACT

The invention relates to a process for manufacturing an internally cooled valve, said process involving providing an externally at least partly cylindrical semifinished product (2), creating or increasing the depth of an at least partly cylindrical cavity in the semifinished product (2) in a hot-working procedure using a male die such that a valve blank is formed; during the hot-working procedure, a recess on an end face of the male die forms a structure on the bottom of the cavity.

BACKGROUND 1. Technical Field

The present invention relates to a manufacturing method formanufacturing an internally cooled valve, a cooling structure beingmounted in a cavity of the valve, on the valve base. The present methodfurther relates to a valve that has been manufactured using the methodaccording to the invention.

2. Related Art

Internally cooled valves have been known for quite some time, in which acavity extends in the valve stem, and in which via so-called “shakercooling,” sodium transports heat from a valve head in the direction ofthe valve stem, which is cooled by the engine head.

It is likewise known to arrange cooling structures, via insertable valvebases, inside the cavity to improve heat transfer from the valve base tothe coolant in the cavity. However, due to the fact that the material ofthe valve is weakened by a weld seam that joins a separate valve base tothe valve head, valve failure and significant engine damage may occurwhen the weld seam fails and coolant escapes into the combustionchamber, or the entire valve base falls into the combustion chamber. Inaddition, welding represents a technically complicated and costlyprocessing step.

A method is known from Japanese Patent application JP 2016084725 A inwhich a valve blank is produced by rotary swaging, wherein a structuremay be mounted on an inner side of a disk surface beforehand.

A method is known from European Patent application EP 2811126 A1 inwhich a valve blank is formed from a semifinished product by dropforging, the stem of the semifinished product being tapered insubsequent steps.

A method is disclosed in U.S. Pat. No. 2,328,512 A, with which a valvebase of an internally cooled valve may be provided with a structure bymeans of a stamping operation.

U.S. Pat. No. 2,280,758 relates to an internally cooled valve having astructure on an inner side of the valve disk which is intended to divertthe coolant in the direction of an outer side of the valve,

Patent documents CN 202645663 U and DE 102015116009 B3 relate tointernally cooled valves having a cavity that is closed by a cover onthe valve disk surface.

German Patent application DE 102015118495 A1 discloses a method forforming disk-shaped blanks by deep drawing and pressing to form a valve.

SUMMARY

Therefore, it is desirable to have a method with which a coolingstructure may be mounted on an inner side of a coolant cavity in thearea of the valve base, without the need for separate weld seams in thearea of the valve base or the valve head.

According to the present invention, a manufacturing method for aninternally cooled valve is provided which encompasses providing asemifinished product having an at least partially cylindrical exterior,and creating or deepening an at least partially cylindrical cavity inthe semifinished product by heat forming, using a stamp, thus producinga valve blank. According to the invention, the method is characterizedin that the end face of the stamp is provided with at least one recessvia which a structure is formed on a base of the cavity during theforming. The cooling structure is thus impressed into the inner side ofa valve base from above, through an area that is subsequently formedinto a valve stem. At a later time, the portion that subsequently formsthe valve stem is reduced in diameter, so that a cavity is present inthe subsequent valve, which has a larger diameter in the valve head thanin the valve stem. By use of this method, any type of weld seam in thearea of the valve head or the valve base may be dispensed with. Inbrief, the method may be described as impressing a structure into thecavity in the area of the valve base, followed by a step of forming aportion of the valve blank into a valve stem, without substantiallychanging the structure in the valve base.

This initial step may be directly applied during forming from adisk-shaped or cylindrical semifinished product, the disk-shaped orcylindrical semifinished product being formed into a bowl-shaped valveblank. However, for a semifinished product that is already bowl-shaped,it is also possible in a further machining step to impress the coolingstructure into the valve base, and likewise to at least partially deepenthe depression.

In one exemplary embodiment of the manufacturing method for aninternally cooled valve, the forming encompasses backward extrusion. Insuch a design, a valve blank may be pressed from an essentiallycylindrical or disk-shaped semifinished product in a single step.Further machining steps are then used to form a valve or disk valve fromthe valve blank, and a coolant such as sodium is introduced into thecavity of the valve or disk valve.

In another exemplary embodiment of the manufacturing method, the formingencompasses forging. A valve disk may likewise be integrally formed byforging as well as by backward extrusion.

In an additional embodiment of the manufacturing method, the structureincludes cooling ribs that extend in a circular or star shape. Thecooling ribs extend in a circular or star shape from an axis of thevalve blank.

Another embodiment of the manufacturing method uses a stamp whichpresses a structure, in the form of pins, cones, or truncated cones,into the cavity at the valve base, which act as cooling elements. Inparticular cooling elements having the shape of a rod, cone, ortruncated cone may allow high heat transfer due to their large surfacearea. It is likewise provided to preferentially use truncated cones atan edge of the piston base, and to use conical cooling elements in themiddle. A conical cooling element situated on the axis of symmetry ofthe valve or valve blank may also achieve rerouting of the coolant flowfrom a movement in an axial direction to a movement in a radialdirection, toward the disk edge, to improve the cooling of the valvehead.

In another embodiment of the manufacturing method, the structureincludes guide blades which can set a coolant in the valve, moving inthe cavity, into rotation about an axis of symmetry of the valve. Theguide blades may be arranged similarly as with a radial compressorturbine.

In another embodiment, the method may also include integral forming of avalve head onto the valve blank during or after the forming. A lowerportion of the semifinished product or valve blank is hereby broadenedand shaped into a valve disk or valve disk edge.

In another embodiment of the manufacturing method for an internallycooled valve, after the valve head is formed, a diameter of the valveblank next to the valve head is reduced in the axial direction, thusforming a valve stem. The bowl-shaped valve blank must undergo furtherforming in order to be used as a disk valve. The invention is based onthe fact that a depression having a large diameter, larger than thesubsequent valve stem diameter, is pressed into a semifinished product,wherein a structure that improves cooling of a subsequent valve base ispressed in at the base of the depression. It is particularlyadvantageous when the subsequent cavity in the valve has a particularlylarge diameter to allow a particularly large amount of heat to beabsorbed by the valve base. Due to the large diameter of the depression,the proposed method allows cooling structures to be mounted or impressedon the inner side of the valve base, since at this location a smallratio of diameter to height of the stamp allows a large transmission offorce. This is not possible with conventional hollow valves, since thestamp that is necessary for this purpose has a length-to-diameter ratiothat is too unfavorable, and during a stamping operation could yield tothe side.

In another embodiment of the manufacturing method for an internallycooled [valve,] the valve stem is formed by section rolling or rotaryswaging, preferably by hot hammering or cold hammering on a mandrel. Theforging tool imparts radial blows to the workpiece, resulting in asmaller cross section of the machined workpiece. Elongation of thematerial results in higher quality than with machining. By usingmandrels, it can be ensured that a cavity in the interior of theworkpiece has a desired inner diameter.

In another embodiment, the manufacturing method includes rolling orcross wedge rolling on a mandrel, the valve stem being formed by therolling.

According to another aspect of the present invention, an internallycooled valve is provided that has been manufactured using one of theabove methods.

THE DRAWINGS

The present invention is explained below with reference to non-limiting,schematic figures.

FIGS. 1A through 1F illustrate sectional views of various segments formanufacturing an internally cooled valve according to the invention.

Identical or similar reference numerals are used in the description andin the figures to refer to identical or similar components or elements.

FIG. 1A shows a sectional view of a cylindrical semifinished product 2that is used as the starting material for manufacturing an internallycooled disk valve.

DETAILED DESCRIPTION

FIG. 1B shows a sectional view of a semifinished product 45 that isformed in the shape of a bowl. The bowl-shaped, formed semifinishedproduct 4 has been formed in the shape of a bowl from above by a stamp,not illustrated. The forming may be carried out as hot forming or coldforming. In the present case, backward extrusion has been used, as theresult of which the height of the formed semifinished product 4 hasincreased greatly compared to the unformed semifinished product 2 fromFIG. 1. Recesses present on the stamp have been impressed as ribs orelevations on the base of the formed cavity. These ribs or elevationsform a cooling structure 6 via which the surface of the depression issignificantly increased, with the aim of increasing heat transfer from asubsequent valve base to a coolant.

A favorable diameter-to-length ratio allows use of backward extrusionwithout the risk of the stamp undergoing lateral deformation.

FIG. 1C shows the bowl-shaped, formed semifinished product 4 that hasbeen further formed into a first valve blank 8. A similar stamp may beused to form a valve head 16 by lateral extrusion and backwardextrusion, the cooling structures 6 still being situated in thedepression. As the result of the lateral extrusion, the diameter of thefirst valve blank 8 in the area of the valve head 16 may be increased,and in this step the thickness of the valve base 18 is also greatlyreduced. Via a backward extrusion component, it is possible at the sametime to increase the length of a stem section 20, wherein the diameterof the stem section is not increased.

It is likewise possible to form the semifinished product from FIG. 1Adirectly into the first valve blank 8. Thus, the first valve blank 8 mayalso be formed from an essentially cylindrical semifinished product in asingle step, wherein in such a method the step illustrated by FIG. 1B isskipped or omitted.

FIG. 1D shows the first valve blank 8, which has been further machinedby rolling, cross wedge rolling, or hammering in the stem area 22 inorder to decrease the diameter of the stem and increase the length ofthe stem, for which reason a second valve blank 10 has been produced. Inthis machining step as well, there is little or no deformation of thecooling structures 6.

FIG. 1E shows the second valve blank 10 from FIG. 1D, which has beenfurther machined by rolling, cross wedge rolling, or hammering in thestem area 24, as the result of which the diameter of the stem 24 hasbeen further decreased, and the length of the stem 24 has been furtherincreased. Due to these work steps, the second valve blank 10 has beenformed into a third valve blank 12. In this machining step as well,there is little or no deformation of the cooling structures 6 in thearea of the valve base 18 of the cavity 30.

FIG. 1E shows the third valve blank 12 after further machining byrolling, cross wedge rolling, or hammering in the stem area 24, and inthe transition to the valve disk 16. An outer diameter of the valve stem26 may be brought to, or virtually to, the final dimensions in the laststep. The stem or the cavity 32 or the depression may now be filled witha coolant (not illustrated), and the cavity closed. Reducing thediameter of the stem 26 also increases the length of the stem 26 up toor beyond the final dimensions. In addition, the stem and the valve headmay undergo final machining or grinding. The cooling structures 6 in thearea of the valve base 18 of the cavity 30 have also been easily formedduring the last work steps. Overall, however, a fairly large cavity thatis additionally provided with cooling structures 6 still remains in thearea of the valve head 16, and the cooling structures allow greater heattransfer from the valve base to a coolant in the cavity 32.

The claims define the scope of protection.

1-11. (canceled)
 12. A method for producing a valve blank for aninternally cooled valve, comprising providing a semifinished producthaving an at least partially cylindrical exterior, and creating an atleast partially cylindrical cavity in the semifinished product by heatforming, using a stamp, thus producing a valve blank, wherein the hotforming encompasses backward extrusion, wherein a structure is formed ona base of the cavity during the hot forming via a recess at n end faceof the stamp.
 13. The method for producing a valve blank according toclaim 12, wherein the structure includes cooling ribs that extend in acircular or star shape.
 14. The method for producing a valve blankaccording to claim 12, wherein the structure includes pins, cones, ortruncated cones that act as cooling elements.
 15. The method forproducing a valve blank according to claim 12, wherein the structureincludes blades that are able to set a coolant in a valve into rotation.16. The method for producing a valve blank according to claim 12,wherein a valve head is formed onto the valve blank during the hotforming.
 17. A method for manufacturing an internally cooled valve,wherein after the valve head is formed according to claim 16, a diameterof the valve blank next to the valve head is reduced in the axialdirection in order to form a valve stem.
 18. The method formanufacturing an internally cooled valve according to claim 17, whereinthe valve stem is formed by rolling or rotary swaging.
 19. The methodfor manufacturing an internally cooled valve according to claim 17,wherein the valve stem is formed by rolling or cross wedge rolling. 20.An internally cooled valve that is manufactured using a method accordingto claim
 12. 21. The method for manufacturing an internally cooled valveaccording to claim 17, wherein the valve stem is formed by hot hammeringor cold hammering on a mandrel.
 22. The method for manufacturing aninternally cooled valve according to claim 19, wherein the valve stem isformed by rolling on a mandrel.